The control system of a brushless motor typically includes a controller that generates control signals for exciting phase windings of the motor. The controller may control phase excitation in response to one or more input signals. For example, the controller may monitor a temperature signal and halt phase excitation should the temperature exceed a threshold.
For an analog input signal, the controller must first convert the analog signal into a digital value using an analog-to-digital converter (ADC). Unfortunately the time required by the ADC to sample the analog signal may delay the execution of other routines by the controller. As a result, the times at which the control signals are generated may be delayed. Any delay to the control signals may adversely affect the performance of the motor system, particularly when operating at relatively high speeds. A possible solution to this problem would be to use a controller having a faster ADC. However, this then increases the cost of the controller. An alternative solution would be to suspend phase excitation when sampling the analog signal. However, suspending phase excitation is likely to affect the performance of the motor system. Additionally, the controller would not then be able to respond quickly to changes in the input signal.